1. Field of the Invention
Generally, the present disclosure relates to the field of the manufacture of integrated circuits and semiconductor devices, and, more particularly, to the measurement of leakage currents occurring in manufactured integrated circuits and devices.
2. Description of the Related Art
The fabrication of advanced integrated circuits, such as CPUs, storage devices, ASICs (application specific integrated circuits) and the like, requires the formation of a large number of circuit elements on a given chip area according to a specified circuit layout. In a wide variety of electronic circuits, field effect transistors represent one important type of circuit element that substantially determines performance of the integrated circuits. Generally, a plurality of process technologies are currently practiced for forming field effect transistors, wherein, for many types of complex circuitry, MOS technology is currently one of the most promising approaches due to the superior characteristics in view of operating speed and/or power consumption and/or cost efficiency. During the fabrication of complex integrated circuits using, for instance, MOS technology, millions of transistors, e.g., N-channel transistors and/or P-channel transistors, are formed on a substrate including a crystalline semiconductor layer.
Integrated circuits comprising such complex devices of a great variety have to be tested for operation before they can be shipped. In fact, ICs are tested and characterized at different stages of the overall manufacturing process. The test and characterization data can be used to grade the performance of the ICs, and to eliminate ICs that fail to meet performance standards set by a manufacturer. For example, one class of tests is performed when the ICs are fully formed, but have not yet been diced into individual chips. The test results are analyzed, and the ICs that fail to meet the required performance standards are discarded when the wafer is diced.
After the ICs are cut from the wafer and separated from each other, and after the ICs that failed the wafer sort test have been eliminated, the remaining ICs are assembled into their packages. The assembly process may involve attaching bond wires or solder bumps to the I/O bonding pads of the IC, connecting the IC to a substrate, and enclosing the IC in a protective package. Once assembly is complete, another set of final tests may be performed. At final test, automated test equipment (ATE) tests the performance of the fully assembled ICs, and, as with the wafer sort test, ICs that fail to meet the performance standards set by a manufacturer are discarded. One common parameter that is tested prior to shipping an IC to a customer is the input leakage current. Input leakage current refers to the static current drawn at an input. Normally, this measurement is made using a precision measurement unit (PMU). If any I/O on an IC shows input leakage current in excess of the maximum set by the manufacturer, the IC is discarded.
In particular, in the context of recent low power technologies, it has become of increasing importance to test for/monitor leakage currents such as device leakages and wiring leakages. Due to the vast plurality of leakage paths in present ICs, leakage parameters may contribute with about 30-40% to the overall monitored electrical para me ers.
Currently the measurement of leakage current parameters is usually performed by applying a constant voltage and measuring the current in autorange mode. Autorange mode is required, since the expected value may be in a very wide range, from some pA up to μA. Therefore, recent instruments must change their measuring range during measurement, which is very time consuming. Usual measurement times are in the range of some 200 ms. In typical parameter measurement programs, the leakage current parameters measurement time sums up to about 20 min per wafer, which is significant and requires reduction. During data evaluation, the leakage current parameters are evaluated on a logarithmic scale. It should be noted that the exact value, i.e., the mantissa of the value, is less important than the order of magnitude. Thus, leakage current parameters are required to be measured very exactly.
In view of the situation described above, the present disclosure provides techniques for determining leakage currents over a wide range of magnitudes of the current strengths with reduced measurement times as compared to the art.